In Ocarina of Time, Rauru is the first person Link meets after having been sealed in the Temple of Light for seven years. The wise old sage tells Link that after he was sealed away, Ganondorf entered the Sacred Realm and touched the Triforce. The sacred golden triangles split apart, leaving Ganondorf with only the Triforce of Power, but still powerful enough to conquer Hyrule and turn it into a land of despair, of which he became the ruler of after usurping Hyrule's Throne. Rauru tells Link that the only way to stop the Evil King is to awaken the five other Sages in the five temples of Hyrule. Before he sends him out into the world do fulfill this dangerous task, he gives him the Medallion of Light, adding his power to Link's.

After Link has awakened all the five other sages, Rauru telepathically contacts Link and tells him that someone is waiting for him in the Temple of Time. Later, together with the other sages, Rauru helps create a bridge to Ganon's Castle. Strangely, in the ending, all the Sages except for Rauru can be seen, perhaps indicating that he is incapable of leaving the Temple of Light.

In the Ocarina of Time manga, Rauru is only a spirit who lives on in the Chamber of the Sages. He also tells Link that Link was born into the guardian house that served the King of Hyrule. He goes on to say that Link's father was killed in battle and his mother brought him to the Great Deku Tree.

It is believed by many that Rauru is the true form of Kaepora Gaebora, the wise owl that helps Link throughout Ocarina of Time. A major reason for this is that a Gossip Stone seen in the game states that Kaepora Gaebora is the reincarnation of an ancient Sage, and Rauru is implied to have been residing within the Temple of Light for ages, awaiting the time when the Sacred Realm would be opened. It would seem this theory would be refuted by Kaepora Gaebora's statement late in the game that he thought that the tales of the Hero of Time were "merely a legend."

However, it is a high possibility that over time, Rauru had been waiting in the Temple of Light for the Hero of Time for so long that he eventually began to believe the Prophecy of the Great Cataclysm was merely a legend that would quite possibly never come to pass (especially since the Sacred Realm's gateway was sealed by the Master Sword, which could only be removed by one of pure heart), not too unlike the legends of the end of the world in the real world. Had he been waiting in the Temple of Light for centuries as he implied, it would explain why Kaepora Gaebora had grown skeptical that the Great Cataclysm would ever actually happen (and by extension the legends of the Hero of Time), and it would also explain why Rauru did not appear with the other Sages at the end of Ocarina of Time, because he could only exist in the form of Kaepora Gaebora outside the Temple of Light. Some things supporting this theory include:

As mentioned before, a Gossip Stone states that Kaepora Gaebora is the reincarnation of an ancient Sage, and the Sage known to have been around the longest of any was Rauru, the Sage of Light.

Rauru seems to already know Link's name when he meets him in the Chamber of Sages seven years after Link pulled the Master Sword from the Pedestal of Time and it seems logical the only way he could have known Link's true name was if he had met him before, which Kaepora Gaebora did.

The other Sages are last seen overlooking a celebrating Hyrule atop Death Mountain at the end of the Imprisoning War, with Rauru nowhere to be seen; However, Kaepora Gaebora was seen in the exact same place earlier in the game.

This would explain Rauru's never appearing in his Hylian form in Hyrule itself (as well as his absence from being with the other Sages at the Imprisoning War's end), since he could only appear outside the Sacred Realm henceforth as the seemingly immortal owl, Kaepora Gaebora.

This would also explain why Rauru did not have to be awakened by the Hero of Time, because he remained active across time as Kaepora Gaebora.

Rauru's robes are the same color as Kaepora Gaebora's feathery body, and his facial expressions greatly mirror those of Kaepora Gaebora.

Kaepora Gaebora seems to hold extensive knowledge about Hyrule and its history, and only someone that had been around for ages would seem to know as much about Hyrule as he did; One of the only people known to have been around that long in the game was Rauru himself.

Rauru would still be alive before Link had taken the Master Sword. This means that the Owl is more like a projection of Rauru from the Sacred Realm into the Light World, much like Ganon had done with Agahnim in The Legend of Zelda: A Link to the Past.